The Open Mobile Architecture (OMA) put forward Converged IP Messaging (CPM) in 2005, in order to realize the inter-working of multiple messaging services, provide a unified messaging service and perfect, consistent and convenient messaging service experience. The CPM converges multiple existing messaging services, comprising Instant Message (IM), Push-To-Talk over Cellular (POC), Mobile E-Email (MEM), Short Messaging Service (SMS), Multimedia Messaging Service (MMS), etc.
At present, the OMA is specifying CPM V1.0. The CPM may be in the following service modes: pager-mode based CPM, session-mode based Large Message Mode CPM, and other session based CPM session services. Before normally using these services, a user needs to log in to a CPM system, i.e., generally called “online”.
A Session Initiation Protocol (SIP) message is adopted to transmit a pager-mode message between a CPM Client and a CPM Enabler which are respectively at sending and receiving ends. The sender cannot use a SIP message for carrying a large message mode CPM message whose size exceeds a limit (for example, over 1300 bytes) when needing to send such a CPM message.
A CPM user can send a CPM pager message to a CPM Ad-hoc group or a CPM Pre-defined group but cannot use a SIP message for carrying such CPM pager message when the size of this message exceeds a certain limit.
In the existing specifications, the solution of sending a large message mode CPM message to a non-CPM system user (i.e. non-CPM user) in an ad-hoc group or a pre-defined group has not been provided yet.